​Prozac Makes Some Fish Become Homicidal

Prozac is used by millions of people as an anti-depressant, but scientists at the University of Wisconsin-Milwaukee found that when fish are administered the drug, they became homicidal.

The study also reveals that human medications are ending up in waterways and creating ecological effects. Anti-depressant drugs are the most commonly prescribed drugs in the United States, about 250 million prescriptions are filled every year. They’re also the most-documented drugs contaminating waterways.

Traces of the drugs typically get into the water when people excrete them. Sewage-treatment plants discharge the filtered effluent, but most aren’t equipped to filter out the drugs. The scientists wanted to study the effects of this drug exposure, and chose the fathead minnow, a fish common fish in Midwest waterways, as their subject. Rebecca Klaper, an ecologist at the University of Wisconsin-Milwaukee’s Great Lakes Water Institute, presented results of the study at the meeting of the North American division of the Society of Environmental Toxicology and Chemistry in Long Beach, California.

Fathead minnows usually display complex mating behavior, with males building the nests where females comes to lay their eggs.

After they’re laid, the males fertilize them and keep watch, cleaning away fungus and dead eggs.

Klaper said that the fluoxetine, the active ingredient in Prozac, was given in very low concentrations – 1 part per billion – which
is the same as that found in waste water discharged into waterways.

The male of the species spent more time hiding alone, hunting and ignoring females.

Female fathead minnows seem to be unaffected by the chemical except for producing fewer eggs.

When the concentration of fluoxetine was increased to the highest levels found in waterways, male minnows started to spend more time building their nests. Scientists increased the dose tenfold, in an effort to see what might happen in our waterways in the future, and the males “become obsessive, to the point they’re ignoring the females,” Klaper said.

When fluoxetine concentrations are increased again, fathead minnows stop reproducing all together and turn violent: “The males start killing the females,” said Klaper.

Strangely, if the females are introduced a month after the males are exposed to the chemical, the males don’t show aggressive behavior
towards them – but the females still don’t lay any eggs.

The research has shown that exposure to the drug can alter the genes responsible for building fish brains and controlling their behavior.